Part: Part Five - Betting Before the Flop

Facing a four-bet with A-K

Pre-flop
Blinds 100 / 200Pot 5,500 (27.5 BB)BTNAK 20,000 (100 BB)YOUyou 3-bet to 1,800CO 20,000 (100 BB)4-bettor4-bets 5,200 (26 BB)SB 20,000 (100 BB)posts 100 (0.5 BB)BB 20,000 (100 BB)posts 200 (1 BB)D

A player opens the cutoff, you three-bet the button to 1,800 with A♥K♠, and he four-bets to 5,200. You're 100 BB deep against an aggressive opponent.

He four-bets to 5,200 (26 BB). With A-K, 100 BB deep vs an aggressive four-bettor, best?

WhyAn aggressive four-betting range is stuffed with A-Q, worse, and outright bluffs, and against that A-K has both the equity and the fold equity to jam - you win it outright or get in flipping or dominating. Flatting means playing a huge pot out of position on a guess, and folding a hand this strong to a wide four-bettor bleeds away a clear edge.
What happensYou shove and he snaps with Q-Q. The board bricks and you lose a big pot. It stings - but with his four-bet range this wide, jamming A-K was correct the instant you did it; a coin flip lost doesn't turn a +EV shove into a mistake.
Against an aggressive four-bettor A-K is too strong to fold and plays best as a five-bet jam - and when it's called and loses the flip, it was still the right shove. His tendencies and the stacks set the play, not the outcome of one hand.

A-K against a four-bet from an aggressive player is usually a get-it-in hand - jamming captures fold equity and keeps live equity, which beats folding a premium or flatting into a bloated out-of-position pot.